Okay, whats the proper way to measure backspacing?

I thought the actual backspacing is measured from the "inside" of the rim (where the tire bead seals...).

I measured my bare ralleys here, and that where the 8" measurement comes from (they are 9" overall with the lip).

If I measure backspacing with a straight edge across the rim, I am now adding also that outer lip of the wheel...

IE, an 8" wheel with 4" backspacing should have the mounting surface (axle) perfectly centered in the wheel... But, it I lay the straightedge across and measure 4 inches, I will have 5 inches out the outside...

Maybe I am confused...

It you used the outer lip, then different wheel types and brands would differ...

As I understand it from past post on the subject, Our Chevelle wheels are old school and are measured from the bead. But if you want to order some of the 17, 18, 19, or 20 inch after market alloy wheels they want to use the new math and measure from the back of the wheel for back space and off set.

Every wheel manufacturer that I've seen actually provide directions for measuring backspacing said the same thing: Measure from the rim edge down to the mounting surface. For instance, in the Weld Wheels catalog, "Rear Spacing" is specifically defined as "the distance from the backside of the wheel mounting pad to the outside rim flange." An 8 inch rim will be centered (i.e. 0 offset) when it has 4.5" of backspacing. This is standard stuff. I've never heard of measuring from the bead instead of the rim edge...it would make no sense.